An Observational Heat Budget of the Swinomish Clam Garden

Clam gardens are a traditional resource management technology that have been used by the Indigenous communities of the Pacific Northwest for at least 3,500 years. A clam garden is built by constructing a low rock wall in the intertidal zone, which through sediment accumulation over time extends the favorable habitat for clams. Not only do clam gardens increase yield of shellfish, but they are also culturally important, providing food security and strengthening communities. However, the physical properties that govern this observed increased clam productivity have not been quantified using Western scientific methods. A two-week field campaign was conducted in June 2024 at the clam garden recently constructed by the Swinomish Indian Tribal Community (SITC), located on Kiket Island, Washington. This intertidal clam garden experiences a tidal range of -0.75m to 3.8m during spring tides, which results in garden transitioning from being completely submerged to fully exposed in one tidal cycle. Over the deployment, recorded water temperatures ranged from 11°C to 18°C, with sharp spikes occurring after low water during spring tides. This pattern is likely due to bed and surface heating of a small volume of water at low tide, followed by rapid cooling as offshore water floods the clam garden. This is critically important to poikilothermic clams, whose metabolism and survival depends on water temperatures, with extremes causing fatality. Therefore, understanding the drivers of temperature variability within the garden is essential. To quantify the sinks and sources of heat in this intertidal system, and to calculate total heat content at varying tidal stages, we used in situ temperature and meteorological data in the framework of a heat budget. Heat content and surface flux terms have been resolved, but the budget remains unclosed. This could be due to bed heating at low tide or advective mechanisms, both of which can be investigated with further analysis. Understanding heat flux dynamics at this site supports Indigenous resurgence by quantifying the physical factors that influence temperature variability and ecological processes in a Western scientific context. This information will aid SITC, along with other communities building clam gardens, by providing physical context helpful for clam garden management, site selection and restoration. [An explanation of the poster is included in the Notes section of the slide.]